OpenGL ES: A Gentle Introduction - Beginning Android Games - page 320

this .hasTexCoords = hasTexCoords;
this .vertexSize = (2 + (hasColor?4:0) + (hasTexCoords?2:0)) * 4;
ByteBuffer buffer = ByteBuffer. allocateDirect (maxVertices * vertexSize);
buffer.order(ByteOrder. nativeOrder ());
vertices = buffer.asFloatBuffer();
if if(maxIndices > 0) {
buffer = ByteBuffer. allocateDirect (maxIndices * Short. SIZE / 8);
buffer.order(ByteOrder. nativeOrder ());
indices = buffer.asShortBuffer();
} else {
indices = null ;
}
}
In the constructor, we specify how many vertices and indices our Vertices instance can
hold maximally, as well as whether the vertices have colors or texture coordinates. Inside the
constructor, we then set the members accordingly and instantiate the buffers. Note that the
ShortBuffer will be set to null if maxIndices is 0. Our rendering will be performed nonindexed in
that case.
public void setVertices( float [] vertices, int offset, int length) {
this .vertices.clear();
this .vertices.put(vertices, offset, length);
this .vertices.flip();
}
public void setIndices( short [] indices, int offset, int length) {
this .indices.clear();
this .indices.put(indices, offset, length);
this .indices.flip();
}
Next up are the setVertices() and setIndices() methods. The latter will throw a
NullPointerException in case the Vertices instance does not store indices. All we do is clear
the buffers and copy the contents of the arrays.
public void draw( int primitiveType, int offset, int numVertices) {
GL10 gl = glGraphics.getGL();
gl.glEnableClientState(GL10. GL_VERTEX_ARRAY );
vertices.position(0);
gl.glVertexPointer(2, GL10. GL_FLOAT , vertexSize, vertices);
if if(hasColor) {
gl.glEnableClientState(GL10. GL_COLOR_ARRAY );
vertices.position(2);
gl.glColorPointer(4, GL10. GL_FLOAT , vertexSize, vertices);
}